Vapor phase chlorination of 1,1-dichloroethane

ABSTRACT

In the preparation of methylchloroform by vapor phase chlorination of 1,1-dichloroethane, the formation of undesirable chlorohydrocarbon reaction products is suppressed by conducting the vapor phase reaction in the presence of a controlled amount of elemental oxygen.

BACKGROUND OF THE INVENTION

This invention relates to an improvement in the known process forpreparing methylchloroform (1,1,1-trichloroethane), a commonly useddegreasing solvent, by reacting chlorine and 1,1-dichloroethane in thevapor phase. In addition to methylchloroform, the vapor phasechlorination produces hydrogen chloride, vinylidene chloride, vinylchloride, unreacted 1,1-dichloroethane, 1,1,2-trichloroethane,1,2-dichloroethylenes and other higher chlorinated hydrocarbons. Bothvinyl chloride and vinylidene chloride may be separated from thereaction mixture and catalytically hydrochlorinated, utilizing theliberated hydrogen chloride, to 1,1-dichloroethane and methylchloroformrespectively. The 1,1,-dichloroethane may be recycled to thechlorination feedstock and the methylchloroform may, of course, becombined with the methylchloroform separated from the original reactionmixture.

Since the remaining reaction products, i.e., 1,1,2-trichloroethane,1,2-dichloroethylenes and higher chlorinated hydrocarbons, are notreadily and economically separated or converted to useful products, itis desirable to suppress the formation of these undesirable reactionproducts. In a typical vapor phase chlorination of 1,1-dichloroethane,it has been found that about 30 or more pounds of these undesirablechlorohydrocarbon reaction products are produced per 100 pounds ofmethylchloroform product.

Methylchloroform product as used herein refers to the methylchloroformproduced directly by the vapor phase chlorination of 1,1-dichloroethaneas well as methylchloroform that would be produced were the vinylidenechloride produced by the vapor phase chlorination of 1,1-dichloroethanecatalytically hydrochlorinated to methylchloroform.

DESCRIPTION OF THE INVENTION

According to the invention, in the production of methylchloroform byvapor phase chlorination of 1,1-dichloroethane, it has been found thatthe formation of undesirable chlorohydrocarbon reaction products issuppressed by conducting the vapor phase reaction in the presence of acontrolled amount of elemental oxygen. As used herein, the termundesirable chlorohydrocarbon reaction products means chlorohydrocarbonreaction products other than methylchloroform, vinyl chloride andvinylidene chloride. Undesirable chlorohydrocarbon rection productstypically produced in the vapor phase chlorination of 1,1-dichloroethaneinclude, for example, 1,1,2-trichloroethane, cis- andtrans-1,2-dichloroethylenes, trichloroethylene, perchloroethylene andhigher chlorinated hydrocarbons.

Oxygen may be fed directly to the reaction zone of a vapor phase reactorbut is preferably fed to the reactor in admixture with the gaseouschlorine and vaporized 1,1-dichloroethane. Gaseous feed mixtures ofchlorine and 1,1-dichloroethane containing up to about 600 parts permillion (ppm) of elemental oxygen were tested under vapor phase rectionconditions and the quantity of undesirable chlorohydrocarbon reactionproducts produced was found to be significantly less than the vaporphase reaction conducted in the absence of oxygen, reaction conditionsbeing identical in all cases.

Although no precise limits of oxygen concentration have been formulated,it is believed that too high an oxygen concentration might poison thereaction whereas too low an oxygen concentration would not be asbeneficial in suppressing the formation of undesirable chlorohydocarbonreaction products.

It is contemplated that under those reaction conditions and reactantratios at which the vapor phase chlorination of 1,1-dichloroethane istypically carried out, oxygen concentrations useful in the practice ofthis invention would be in the range of from about 100 to about 600 ppmoxygen, preferably from about 150 to about 500 ppm oxygen and mostpreferably from about 200 to about 400 ppm oxygen. Although the optimumlevel of oxygen concentration may vary somewhat depending on reactionconditions and reactant ratios, the same may be readily determined bypre-selecting the desired reaction conditions and reactant ratio andmaking a series of runs in the presence of measured, incremental amountsof oxygen.

Although elemental oxygen is preferably used according to the invention,the oxygen may be added in the form of atmospheric air.

In accordance with a preferred embodiment of the invention, a gaseousmixture of 1,1-dichloroethane, chlorine and oxygen is introduced into asuitable reactor. The reactor is preferably of the plug flow type, i.e.,one in which there is no substantial degree of back mixing between theproduct gas stream and the feed gas stream. The conditions under whichthe reaction is conducted may vary over a wide range. The pressure isselected so as to provide optimum contact of the reactant gases withminimum residence time in the reactor. At temperatures below about 350°C., conversion rates are usually undesirably low whereas temperaturesabove about 550° C. may result in excessive carbonization and productdegradation.

The vapor phase reaction is typically conducted at a temperature ofbetween 350° C. and 550° C., preferably from about 400° C. to about 500°C., and at a pressure of up to about 120 psig, preferably from about 40to 80 psig. Residence time in the reactor is typically from about 0.5 to5 seconds, preferably from 1 to 2 seconds. The molar ratio of chlorineto 1,1-dichloroethane is typically in the range of from 0.2:1 to 1:1,preferably from about 0.4:1 to 0.8:1.

In a typical practice of the invention, a gaseous mixture of chlorine,1,1-dichloroethane and oxygen are introduced at a pressure of from 40 to80 psig to a plug flow reactor maintained at a temperature between 400°C. and 500° C., the residence time of the gaseous mixture in the reactorbeing about 1 to 2 seconds. The product gas stream from the reactor ispassed in known manner through a first separating means, for example, avacuum distillation column and a first fraction is separated therefrom,said first fraction consisting of hydrogen chloride, vinylidenechloride, vinyl chloride, and trans-1,2-dichloroethylene. The firstfraction is hydrochlorinated in known manner in the liquid phase undersubstantially anhydrous conditions in the presence of a Friedel-Craftscatalyst, such as ferric chloride, to substantially quantitativelyconvert vinylidene chloride to methylchloroform and vinyl chloride to1,1-dichloroethane, the hydrogen chloride being consumed in thehydrochlorination reaction with the trans-1,2-dichloroethylene beingsubstantially unaffected. (Alternatively, vinyl chloride may beseparated as such prior to hydrochlorination.)

A fraction consisting of 1,1-dichloroethane and cis-1,2-dichloroethyleneis separated from the balance of the chlorination product stream and the1,1-dichloroethane is recycled to the vapor phase chlorination feedstockalong with the 1,1-dichloroethane separated from the hydrochlorinationproduct.

Methylchloroform is separated from the balance of the chlorinationproduct and combined with the methychloroform separated from thehydrochlorination product.

It is apparent that many variations in the foregoing typical process maybe made since both vapor phase chlorination of 1,1-dichloroethane aswell as liquid phase catalytic hydrochlorination of vinyl chloride andvinylidene chloride are well known processes, the invention residing inconducting the vapor phase chlorination in the presence of a controlledamount of oxygen in order to suppress the formation of undesirablechlorohydrocarbon reaction products.

The invention is further illustrated but is not intended to be limitedby the following examples.

EXAMPLE 1

A plug flow type reactor was constructed from a 20 foot (6.1 meters)length of 0.25 inch (6.35 millimeters) outside diameter nickel tube. Thetube was formed into a plurality of coils about 6 inches (15.2centimeters) in diameter. The coiled portion of the tube was positionedin a muffle furnace with the free ends of the tubing protruding throughthe walls of the furnace. A gaseous mixture of 1,1-dichloroethane andchlorine was continuously introduced under a pressure of 50 psig (4.55kg/cm²) into one end of the tube, the normally liquid 1,1-dichloroethanehaving first been vaporized in a preheater. The molar ratio of chlorineto 1,1-dichloroethane was 0.7 to 1. The gaseous mixture was passedthrough the coiled portion of the tube that had been preheated andstabilized at the reaction temperature of 450° C., the residence time ofthe gaseous mixture in the reaction being about 1 second. The productgas stream was withdrawn from the other end of the tube, passed througha scrubbing train, collected and analyzed. The analytical results aresummarized in Table I.

EXAMPLES 2 to 6

The procedure described in Example 1 was followed except that measuredincremental amounts of elemental oxygen were added to the gaseous feedmixture. Five runs were made under the reaction conditions specified inExample 1 at a molar ratio of chlorine to 1,1-dichloroethane of 0.7 to 1maintaining oxygen concentrations in the feed gas mixture of 150, 300,300, 450 and 600 ppm, respectively. Analyses of the respective productgas streams are summarized in Table I.

From an inspection of the data, it is readily seen that when1,1-dichloroethane is chlorinated in the vapor phase in the presence ofcontrolled relatively small amounts of elemental oxygen, the sameresults in a substantial reduction in the quantity of undesirablehalohydrocarbon reaction products as compared with the vapor phasechlorination of 1,1-dichloroethane conducted in the absence of oxygenunder identical reaction conditions. In addition, the yield ofmethylchloroform is substantially increased.

Although the invention has been described with specific references toand specific details of embodiments thereof, it is to be understood thatit is not intended to be so limited since changes and alterationstherein may be made which are within the full intended scope of thisinvention as defined by the appended claims.

                  TABLE I                                                         ______________________________________                                        Vapor Phase Chlorination of 1,1-Dichloroethane Effect of                      Oxygen Concentration on Suppression of the Formation of                       Undesirable Chlorohydrocarbon Reaction Products                               Example        1      2      3    4    5    6                                 ______________________________________                                        Oxygen in feed, ppm                                                                          0      150    300  300  450  600                               Reaction products, mole                                                       percent:                                                                      Vinyl chloride 26.1   23.4   24.1 23.8 18.8 23.1                              1,1-Dichloroethane                                                                           8.1    4.9    4.7  5.8  3.2  5.4                               Vinylidene chloride                                                                          46.2   37.5   34.0 27.8 45.7 35.5                              Methylchloroform                                                                             4.9    24.0   27.9 32.8 21.8 24.7                              1,1,2-Trichloroethane                                                                        2.0    0.9    1.1  1.2  0.8  1.7                               cis-1,2-Dichloroethylene                                                                     2.8    2.5    2.3  2.2  2.0  2.6                               trans-1,2-                                                                    Dichloroethylene                                                                             2.4    2.2    2.2  1.7  1.9  2.3                               Tetrachloroethane                                                                            2.6    1.3    1.1  1.5  1.5  1.6                               Trichloroethylene                                                                            3.8    2.2    1.6  2.0  2.8  1.9                               Perchloroethylene                                                                            0.1    <0.1   0.1  0.3  <0.1 0.1                               Pentachloroethane                                                                            --     <0.1   --   <0.1 <0.1 --                                Carbon tetrachloride                                                                         <0.1   <0.1   <0.1 --   <0.1 --                                Unknown        1.0    1.0    0.8  0.7  1.3  1.1                               Pounds UCRP*                                                                  100 pounds MC**                                                                              27.7   16.2   14.5 15.2 15.6 18.5                              ______________________________________                                         *UCRP  Undesirable chlorohydrocarbon reaction products, i.e., those           chlorohydrocarbons other than vinyl chloride, unreacted 1,1dichloroethane     vinylidene chloride and methylchloroform.                                     **MC  Methylchloroform; includes both methylchloroform directly produced      by the vapor phase chlorination as well as methylchloroform that would be     produced were the vinylidene chloride completely converted to                 methylchloroform by liquid phase catalytic hydrochlorination.            

We claim:
 1. In a process for the production of the methylchloroformwherein chlorine and 1,1-dichloroethane are reacted under conditions oftemperature and pressure sufficient to maintain the reactants in thevapor phase, the improvement comprising conducting said vapor phasereaction between chlorine and 1,1-dichloroethane in the presence or acontrolled quantity of elemental oxygen in amounts of up to about 600parts per million parts of chlorine and 1,1,-dichloroethane to obtain areaction product having a higher mole percentage of methylchloroformthan that obtained were the reaction conducted in the absence of oxygenuner the same conditions of temperature and pressure, and at the samereactants ratio.
 2. The improvement of claim 1 wherein oxygen is presentin an amount of from about 100 to about 500 parts per million.
 3. Theimprovement of claim 2 wherein oxygen is present in an amount of fromabout 200 to about 400 parts per million.
 4. In a process for theproduction of methylchloroform comprising feeding of vaporous feedmixture of chlorine and 1,1-dichloroethane to a plug flow reactor andreacting vaporous mixture therein at a temperature and pressuresufficient to maintain the reactants in the vapor phase, the improvementcomprising adding a controlled amount of oxygen to the reactor feedmixture and maintaining an oxygen concentration in the feed mixture ofup to about 600 parts per million parts of feed mixture to obtain areaction product having a higher mole percentage of methylchloroformthan that obtained where the reaction conducted in the absence of oxygenunder the same conditions of temperature and pressure and at the samereactants ratio.
 5. The improvement of claim 4 wherein the oxygencontent of the feed mixture is maintained in the range of from about 100to about 500 parts per million.
 6. The improvement of claim 5 whereinthe oxygen content of the feed mixture is maintained in the range offrom about 200 to about 400 parts per million.